Ketene furnaces



March 5,1951 E. s, PAINTER 2,784,065

KETENE FURNACES Filed April 29, 1954 2 Sheets-Sheet 1 Fig.2

Fig.

T0 STACK EDWIN 5. PAINTER INVENTOR.

March 5, 1957 Filed April 29, 1954 2 Sheets-Sheet 2 CONDENSER STACK EDWIN S. PA/NTE/P INVENTOR.

A 7' TORNE Y5 KETENE FURNACES 'Edwin S. Painter, Kingsport, Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New .lersey This invention relates to an improvement in cracking furnaces for the production of ketene from ketenizable materials such as acetic acid, and it relates more particularly to the addition to more or less conventional type furnaces, of additional louvers or passages for the hot combustion gases, whereby the hot gases are directed to the coils in the heating chambers at locations intermediate between the ends of these coils.

It is known that acetic acid and other ketenizable substances can be converted to ketene by passage through a series of coils of tubing heated to temperatures in the range of 700 C. and above. Apparatus for accomplishing this conversion is well known, as for example, in U. S. Patents Nos. 2,232,705, 2,393,778, and 2,541,471. In the latest issued of these three patents, for example, the basic construction which has been improved upon by the present invention is shown, there being a combustion chamber from which hot gases flow into one end of a pyrolysis chamber and then flow in zigzag fashion through a superheat chamber and a preheat chamber. These chambers contain serially connected coils of tubing known as the pyrolysis, superheat, and preheat coils, respectively. The material to be converted to ketene is passed into the inlet of the preheat coil and from the outlet of this coil to the superheat coil, from which it flows to the pyrolysis coil and then from the outlet of this coil to suitable condensing and other apparatus. Such appartus for condensing and the like is shown, for example, in U. S. Patent No. 2,232,705.

I have found that this known type of ketene furnace can be improved by the addition of louvers or passages between the combustion chamber and the pyrolysis chamber, these louvers being located approximately centrally between the ends of the pyrolysis chamber so as to direct the hot gases onto a central portion of the pyrolysis coil in this chamber, while the normal flow of hot gases also takes place to the lower end of this coil. Additional passages for the flow of hot gases are also provided at a similar location in the wall which separates the superheat chamber from the preheat chamber, thus providing, in addition to the regular flow of gas to the lower end of the preheat coil, an additional flow of hot gases to a central portion of the preheat coil. The practice of this invention is quite advantageous in lowering the velocity of hot gases which would normally impinge upon relatively small areas of the pyrolysis and preheat coils, and the results of the use of our invention include substantial decreases in localized erosion and oxidation in this region of the coils. Such erosion and oxidation at localized points have been frequent causes of failure of the coils in the past. In the case of the directing of part of the hot gases onto a central portion of the preheat coil, 1 have found that a much more rapid preheating of the material passing through the coil is thereby achleved.

My invention also has particular utility in connection with the improvement in ketene furnaces described and claimed in my copending patent application with Louis ted States Patent i 2,784,065 Patented Mar. 5, 19 57 ice G. Haller, Serial No. 325,086, filed December 10, 1952. In this copending application there is described an improvement wherein the preheat coil is divided into two sections, each of which has a separate inlet and outlet. The superheat and pyrolysis coils may each remain a single coil as in the case of Patent No. 2,541,471, with one of the preheat coil sections being connected to feed the superheat coil and the other preheat coil section being connected to feed the pyrolysis coil. This copending application also describes a particularly advantageous arrangement wherein each of the three coils is divided into two sections, thus providing two separate and distinct flows of material through the furnace, resulting in a considerable increase in the capacity of the furnace. In these improved arrangements shown and claimed in the copending application just referred to, my present invention has particular utility, in that the upper coil sections in the preheat and pyrolysis chambers receive what might be called their own direct feeds of hot combustion gases rather than receiving only the flow of hot gas which has already passed over the lower coils in these chambers. This allows the increase in capacity made possible by the split-coil construction of the copending application to be more fully utilized and considerable heat savings have been effected.

It is an object of my invention to provide improved efliciency in a ketene furnace by the addition of louvers or hot gas passages to existing type furnaces whereby portions of the hot gas go directly to central locations, in the pyrolysis and preheat chambers. A further object of the invention is to provide improved operation of the split-coil arrangement as described and claimed in my copending application referred to above.

These and other objects of the invention will be apparent from a study of the following specification when read in conjunction with the accompanying drawings, in which:

Fig. l is a semidiagrammatic longitudinal sectional view taken on line 1-1 of Fig. 2, being partly in elevation and partly on exaggerated scale for clarity, and showing a ketene furnace utilizing my invention;

Fig. 2 is a horizontal sectional view taken on line 22 of Fig. 1; and

Fig. 3 is a view similar to Fig. 1 but showing a modified type of coil arrangement such as is shown in Fig. 4

of Painter and Haller application, Serial No. 325,086, referred to above, and illustrating use of the present invention with this type of coil arrangement.

Turning now to the drawings in detail, I have shown in Figs. 1 and 2 a furnace housing 10 containing a plurality of partition walls 11, 12, 13 and 14, which form a combustion chamber 15, a pyrolysis chamber 16, a superheat chamber 17 and a preheat chamber 18. These chambers, in the normal construction and in the construction shown herein, are connected by passages, the numeral 19 denoting the passages which connect to the lower ends of the combustion and pyrolysis chambers. At the upper end of the pyrolysis chamber are passages 20 through which hot gases pass from the upper end of the pyrolysis chamber to the upper end of the superheat chamber 17. The lower ends of the superheat chamber 17 and the preheat chamber 18 are connected by a passage or passages 21, and a hollow tube 22 is located in the preheat chamber with its open upper end (not shown) positioned near the upper end thereof so that hot gases can pass upwardly around it in the preheat chamber and then downwardly through the hollow member 22 and out to the stack as shown by the legend.

Preheat chamber 18 contains a preheat coil 28 which is connected to superheat coil 29 located in the superheat chamber by means of an external connection 30, and a similar connection 31 connects the superheat. coil 29 with apyrolysis coil 32. The compound to be converted to ketene enters the preheat coil through its inlet 33 and the hot cracked products leave the furnace through an outlet 34, from which they pass to suitable condensing or other apparatus which is not shown and which comprises no part of the present invention.

The portion of the apparatus which has .just been described is conventional. In applying myinven'tion to this furnace construction, I add louvers 36 which comprise passages for hot combustion gases and which pass from the combustion chamber into the pyrolysis chamber at a level approximately midway between the ends of this latter chamber. I also add similar louvers or passages 37 at a similar level in Wall 14 so as to connect the central portion of chamber 17 with a-oentral portion of the preheat'chamber 8. The passages 36 and '37 each are advantageously of an area approximately one-half as great as the area formerly used for the conventional arches or passageways located at 19 and 21. These passageways l9 and 21 are advantageously reduced to about one-half their former size, so that the cross section of passages 19 approximately equals that or" louvers 36, and the same relationship advantageously exist between the cross sections of passages 21 and 37.

By utilizing the improved construction just described, I am able to achieve considerable increases in furnace etficiency in that the heat requirements are lowered. This is the result of more rapid preheating of the material passing through the preheat coil as well as more even heating of the pyrolysis coil 32. I have also :found that whereas formerly the directing of the hot gases to limited areas at the lower ends of the pyrolysis and preheat coils caused considerable localized erosion and oxidation which caused frequent failure of these coils, this erosion and oxidation has been decreased considerably and coil 'life has been correspondingly increased.

Referring now to Fig. 3, I have shown in this figure the present invention applied to the construction of Fig. 4 of my cit-pending application with Louis G. Haller, Serial No. 325,086, filed December 10, 1952. In that construction the furnace it) has a combustion chamber 40 and the wall construction is generally the same as shown in Fig. 1. There is a considerable and highly advantageous change in the coil arrangement in Fig. 3, however, each of the coils being divided into upper-and lower :portions. Thus, the preheat coil comprises a lower portion 28a and an upper portion 28b, the superheatcoil comprises a lower portion 29:: and an upper portion 29b, and the pyrolysis coil comprises a lower section 32a and anlu'pper portion 32b. hese coil sections are connected so that two separate and distinct flow paths are provided, one of which begins with the inlet 41 to'the upper section 28b of the preheat coils, then to upper superheat coil 2%,

then to upper pyrolysis coil 32b, and then out through outlet 42 to the condenser or other apparatus. The other flow path is from inlet 43 to the lower preheat coil section then to the lower superheat coil section 29a and finally to the lower pyrolysis coil section 32a from which the hot cracked products pass through an outlet 44 to condenser or the like.

In applying my invention to this type of coil arrangement, louvers between combustion chamber 40 and the pyrolysis chamber are shown at 43 in parallel with the conventional passages 43a, and the louvers between the preheat chamber and the superheat chamber are shown at 4 9 in parallel with the conventional passages 49a. These louvers in each case are positioned so as to direct the hot gases substantially upon the lowermost coil of the upper coil sections 32b and 2812 respectively. This allows the advantages of the split-coil construction of Fig. 3 to be utilized more fully in that the upper coil sections 32!) and 2812 are better heated by the direct flow of hot gases to them, whereas otherwise the hot gases would only reach the separate coils after passing over the lower coils 32a and 28a, respectively. In addition, the

upper coils in the new construction receive not only the portion of hot gases flowing through the louvers 48 and 49, but also the normal flow of hot gases passing through the conventional connections or passageways 48a and 4%, respectively, with which they are located in parallel.

By means of my invention, the heat requirements of ketene furnaces are substantially reduced, providing a substantial saving in-operating costs. For example, in one furnace utilizing my invention, the heating gas requirements for the furnace have been reduced at a rate of several thousand dollars per year since installation of my invention. In addition, and of considerable importance, an increase :in coil life equivalent to about 30% has been achieved. Not only does this increase in coil life have the rather obvious efiect of reducing the material, labor and loss of production costs entailed in coil replacement, but it also cuts down the periods of reduced yield during which pin hole air leaks in the coils (which are under vacuum) permit entry of oxygen, which causes oxidation and reduces the yields.

My invention also has utility with a construction of the type shown in Fig. l of the copending application referred to above, wherein only the preheat coil is divided into two sections, the upper section being connected to the pyrolysis coil, while the lower section is connected to the superheat coil. In this case, the outlets of both the super-heat and pyrolysis coils may be fed directly to a condenser.

I claim:

1. Ina-furnace for the pyrolysis of .ketenizable material to form keten'e, and wherein a plurality of serially connected elongated coils of tubing through which the material flows are positioned in at least three elongated and parallel heating chambers separated by wall means having openings providing communication between the chambers, 'saidopenings being located so as to direct hot gases from a combustion chamber first to one end of the hottest chamber for how therethrough and then into the opposite end of the next hottest chamber where the direction of flow is reversed, the now of hot gases continuing in zigzag fashion through the chambers, sweeping over the coils in each chamber in a direction parallel to the coil axes, the

improvements comprising the provision of hot .gas passages in the Wall between the combustion chamber and the hottest coil-containing chamber and opening into the last-mentioned chamber in a region located approximately centrally of its length, and the provision of additional hot gas passages at a similar location in the wall separating the next hottest and coolest coil-containing chambers, whereby more even distribution of the hot gases over'the coils is-o'btained and localized erosion and oxidation are reduced.

2. The improvement set forth in claim '1, wherein but a single coil is located in each chamber.

3. The improvement set forth .in claim l, wherein the coiled tubing in at least the coolest chamber is divided into two separate sections located in opposite ends of the chamber and each section having a separate inlet and outlet, the additional hot gas passages for passage of hot gases into this chamber being positioned to join the normal flow of hot gases as the normal flow reaches the second portion of said divided coil to be swept over by said normal flow of hot gases.-

4. The improvement set forth in claim l, wherein the normal and additional hot gas passages of each set are of approximately equal cross-section.

References Cited in the file of this patent UNITED STATES PATENTS 709,655 Webster Sept. 23, 1902 1,959,214 Osenberg May 15, .1934 2,536,949 Livingoocl Jan. 2, 1951 2,541,471 Hull Feb. 13, 1951 

1. IN A FURNACE FOR THE PYROLYSIS OF KETENIZABLE MATERIAL TO FORM KETENE, AND WHEREIN A PLURALITY OF SERIALLY CONNECTED ELONGATED COILS OF TUBING THROUGH WHICH THE MATERIAL FLOWS ARE POSITIONED IN AT LEAST THREE ELONGATED AND PARALLEL HEATING CHAMBERS SEPARATED BY WALL MEANS HAVING OPENINGS PROVIDING COMMUNICATION BETWEEN THE CHAMBERS, SAID OPENINGS BEING LOCATED SO AS TO DIRECT HOT GASES FROM A COMBUSTION CHAMBER FIRST TO ONE END OF THE HOTTEST CHAMBER FOR FLOW THERETHROUGH AND THEN INTO THE OPPOSITE END OF THE NEXT HOTTEST CHAMBER WHERE THE DIRECTION OF FLOW IS REVERSED, THE FLOW OF HOT GASES CONTINUING IN ZIGZAG FASHION THROUGH THE CHAMBERS, SWEEPING OVER THE COILS IN EACH CHAMBER IN A DIRECTION PARALLEL TO THE COIL AXES, THE IMPROVEMENTS COMPRISING THE PROVISION OF HOT GAS PASSAGES IN THE WALL BETWEEN THE COMBUSTION CHAMBER AND THE HOTTEST COIL-CONTAINING CHAMBER AND OPENING INTO THE LAST-MENTIONED CHAMBER IN A REGION LOCATED APPROXIMATELY CENTRALLY OF ITS LENGTH, AND THE PROVISION OF ADDITIONAL HOT GAS PASSAGES AT A SIMILAR LOCATION IN THE WALL SEPARATING THE NEXT HOTTEST AND COOLEST COIL-CONTAINING CHAMBERS, WHEREBY MORE EVEN DISTRIBUTION OF THE HOT GASES OVER THE COILS IS OBTAINED AND LOCALIZED EROSION AND OXIDATION ARE REDUCED. 